GCM-related uncertainty in river flow projections at the threshold for “dangerous” climate change: the Kalu Ganga river, Sri Lanka

Abstract

The Kalu Ganga catchment is one of the largest in Sri Lanka, and is home to 5% of the national population. A first assessment is provided here of the sensitivity of Kalu Ganga runoff to a 2°C increase in global mean temperature–the supposed threshold for “dangerous” climate change. Runoff is simulated using the HBV-Light hydrological model and scenario data from seven general circulation models (GCMs). Precipitation is the strongest cause of change in runoff. Substantial inter-GCM differences in scenario precipitation lead to uncertainty in the direction of change in mean annual runoff from the baseline (range −25% to +19%). Scenario monthly runoff ranges from −41% to +124% of the baseline values at its most extreme (March); June is the only month with a consistent direction of change (range −17% to −65%)–thus indicating that climate change may lead to a substantially different hydrological regime in the Kalu Ganga catchment.